Impact of bladder size and shape on the accuracy of formula method for bladder volume evaluation.

Background: To explore the impact of bladder size and shape on the accuracy of the formula method (V = 0.52 × d₁ × d₂ × d₃) for bladder volume evaluation.

Methods: Data was retrospectively collected from 220 patients without reportable bladder diseases. CT images were imported into 3D Slicer software to measure the bladder volume V_A (reference standards). Bladder volume was also measured by the formula method V_B = 0.52 × d₁ × d₂ × d₃. Results of these two methods were compared based on bladder size and shape.

Results: The bldder volume was 121.0 ± 83.6 mL with the formula method, compared with 128.5 ± 82.6 mL measured by 3D Slicer (P < 0.0001). Patients were divided into three groups based on bladder size, the mean percent deviations between the two methods were 18.8 ± 20.8%, 3.4 ± 12.9% and 4.6 ± 10.6%, respectively. According to the bladder shape, it can be divided into 5 types. For round and triangle shapes, there was no significant statistical difference in the results of the two methods. For bladder shapes with ellipse, rectangle and irregular shape, the volume evaluated by the formula method was statistically lower. Their deviations were 9.7 ± 17.5%, 12.9 ± 9.6% and 14.4 ± 21.2%, respectively.

Conclusion: The accuracy of the formula method for estimating bladder volume is affected by bladder size and shape. Overall, the formula method tends to underestimate the bladder volume. The error of small-sized bladders is much greater than that of large-sized bladders. Furthermore, the formula method has high accuracy in measuring bladder volume with round and triangle shapes.